A blind is mounted to or near a window. Slats of the blind stop sun light from directly projecting through the window into a room, and shield an interior of the room from external environment. Please refer to FIGS. 1 and 2. For the slats of a conventional Venetian blind to tilt by an angle to close the window, a ladder drum A1 is mounted to and in each end of a head rail of the blind, and a ladder cord B1 having the slats held thereto is secured to the ladder drum A1. The ladder drum A1 is associated with a tilt bar C1 in the head rail and can therefore be turned by a desired angle along with the tilt bar under control. When the ladder drum A1 is turned by an angle, slats held to the ladder cord B1 secured to the ladder drum A1 are brought to synchronously tilt by the same angle.
The ladder drum A1 has an axial central shaft A2, and is provided on a top with two securing holes A3. Each of the two securing holes A3 has an expanded end and a reduced end communicable via a narrowed neck portion. To secure the ladder cord B1 to the ladder drum A1, first the two retaining blocks B2 are connected to two free ends of the ladder cord B1. A total of four retaining blocks B2 are needed because there are two ladder cords B1 provided for one Venetian blind. Then, the free ends of the ladder cord B1, which has the slats held thereto, are lead into the reduced ends of the two securing holes A3 via the expanded ends and the neck portion thereof. With the retaining blocks B2 being stopped by and held in the reduced ends of the securing holes A3, the free ends of the ladder cord B1 are secured to the ladder drum A1. When the tilt bar C1 is controlled to turn about an axis thereof, the ladder drum A1 and accordingly, the slats held thereto are brought by the tilt bar C1 to turn a certain angle at the same time.
In the above-described conventional ladder drum A1 for controlling the tilting angle of the slats of a Venetian blind, the retaining blocks B2 are used as stoppers to stop the ladder cord B1 from separating from the ladder drum A1. Generally, the retaining blocks B2 are manually or mechanically connected to the free ends of the ladder cord B1 and then extended through the securing holes A3 to be held to the reduced ends of the securing holes A3. In the event a retaining block B2 is connected to an incorrect position on the ladder cord B1, it must be removed from the ladder cord B1 and be reconnected to thereby increase the labor and time for assembling the ladder cord B1 to the ladder drum A1. The assembling efficiency is therefore lowered.
Moreover, the Venetian blind delivered from the blind manufacturer might be defective due to incorrectly connected retaining blocks B2 on the ladder cord B1. Such defect might not be found until the whole Venetian blind is mounted to a window and it is found the slats thereof are not in a horizontal position. Since some of the parts for mounting the Venetian blind are not reusable once they are dismounted from the blind, the worker has to troublesomely mount another new set of Venetian blinds to replace the defective one.